After demonstrating Band 3, the predominant transmembrane protein in red cell to be responsible for intramembrane particle appearance in liposomes (Yu and Branton 1976), I intend to study possible associations of this protein with other membrane components in the native membrane and to investigate its putative transport function in the reconstituted protein-lipid vesicles. The red cell membranes will be fused with large-sized liposomes. The distribution of various membrane components, as they migrate into the newly fused liposome region, will be studied using immunochemical labeling techniques and freeze-etch electron microscopy. The molecular make-up of intramembrane particles in the native membrane can thus be elucidated through the differential rates of diffusion of various components versus that of intramembrane particles. The putative anion transport activity of Band 3, which is essential for CO2 removal through blood circulation, will be pursued in the reconstituted system. To determine the minimum polypeptide compositions required for such transport, lipid vesicles containing Band 3 and various other membrane components will be prepared. The transport activity will be measured by the uptake of radioactive phosphates in exchange for chloride ions previously trapped inside the vesicles. The kinetic analysis will help to elucidate the molecular basis of transport activity in red cell and will also provide for the first time the evidence of functional reconstitution of human erythrocyte intramembrane particles.